1. Field of the Invention
This invention relates to a suction cup apparatus for attachment to a wall surface, and, more particularly to such an apparatus capable of being securely attached both to porous and nonporous surfaces.
2. Summary of the Background Information
A number of devices are available for attaching objects to walls using suction cups. In the simplest form of such a device, the central portions of one or more suction cups are directly attached to a housing or frame of the device. Each of the suction cups, which are composed of an elastomeric material, includes a concave surface held against the wall. For example, the elastomeric suction cups are pressed into place on the rigid frame of the device, or an elastomeric material may be molded over a rigid plastic frame to form one or more suction cups extending outward from the frame. When the device is pressed toward the wall, a portion of the air held between the concave surface and the wall is pushed outward, past the periphery of each suction cup. Then, after the device is released, as each suction cup tries to return to its original shape while the shape of the suction cup extending to its periphery blocks the inward movement of air, a partial vacuum is formed between the concave surface and the wall, holding the device in place on the wall.
In another type of suction cup device, the central portion of a suction cup is attached to an actuator, while the periphery of the suction cup is held by a ring forming part of the device. First, the periphery of the suction cup is held against the wall with the actuator holding the central portion of the suction cup close to the wall. Then, as the periphery of the suction cup remains against the wall, the actuator is moved so that the central portion of the suction cup is moved away from the wall, increasing the volume of the space between the concave surface of the suction cup and the wall to form a partial vacuum within this space, holding the device in place on the wall. Again, the shape of the suction cup extending to its periphery blocks the inward flow of air.
Both types of suction cup generally work well on hard and smooth wall surfaces, such as ceramic tile, glass, stainless steel, or painted metal. However, when the suction cup is attached to a wall having a porous surface, such as painted gypsum wallboard, the porosity of the wall surface allows a slow leakage of air past the periphery of the suction cup into the space between the concave surface of the suction cup and the wall. This leakage of air reduces the level of partial vacuum within this space, so that the device falls off the wall, typically within a few hours to two weeks after its installation on the wall.